This invention relates to the handling of low temperature hydrocarbon fluid streams. In another aspect, this invention relates to method and apparatus for handling low temperature hydrocarbons in a flare gas relief system.
Safety relief systems are incorporated in essentially all chemical processing facilities. Included in these safety relief systems are pressure vessels provided with pressure relief valves to protect against over-pressure. Generally, the relief valves of these pressure vessels are connected into a common relief header whereby any relief fluids are passed downstream for further processing. In the case where the relief fluids are combustible, they are often passed to a flare system by which they are accumulated and combusted and whereby the combustion products are passed to the atmosphere.
A common problem that often occurs in cryogenic or low temperature processes is the release of low temperature fluid stream into a flare header system. For example, in an ethylene process, an ethylene liquid and gas mixture at its saturation temperature, which can be less than -103.degree. F., is occasionally released into a flare header system that is maintained at a pressure of slightly above atmospheric pressure. Because of low saturation temperature of the ethylene, the piping within the flare system is subjected to extreme cold temperatures. Generally, the release of the ethylene to the flare system is on an intermittent basis and usually releases are done instantaneously or cyclic releases of cold fluids into the flare system can cause either thermal shock or thermal fatigue resulting in failure of the piping system caused by the stresses created from the extreme temperature changes.
Another problem encountered in cryogenic or low temperature processes is the relief of cold fluids into a flare header system that exit a flare stack and that are spewed into the atmosphere without combustion. The release of these cold fluids into the atmosphere has safety implications to personnel and to equipment.